GLACIAL FEATURES OF THE ALPS 3 



of all these phenomena has been recognized, but this conclusion is 

 not in harmony with ideas which prevailed for a considerable period, 

 when only one pari of the irregularities of Alpine valleys was taken into 

 consideration. 



For some time the great Alpine lakes have been regarded as 

 the only irregularities of the Alpine valleys, and the questions of 

 Alpine geomorphology have included only the formation of the great 

 Alpine lakes. Of the different ways in which valley lakes are formed, 

 only two have been considered; namely, the hypothesis of warping 

 and the hypothesis of glacial erosion presented by A. C. Ramsay. 

 In order to understand the former, let us assume that the lower part 

 of a normal river slope was elevated, or the upper part was depressed. 

 The normal slope curve then would be changed into a curve with an 

 ascending part having a reversed slope, and the part limited down- 

 stream by this reversed slope would be filled with water so as to 

 become submerged. This idea, first suggested by Sir Charles Lyell, 

 and later developed further by Rutimeyer and Heim in Switzerland, 

 helps us to understand the transformation of some valleys into lake 

 basins; but it leads to consequences which are not supported by 

 observations in the field. Earth-movements which could reverse 

 the slope curve of a master- river must also affect its branches; and 

 if a part of its curve is depressed to form a basin, the affluents of this 

 part must also be depressed, and their lower courses must be sub- 

 merged in a manner similar to the basin formed by the depression of 

 the floor of the master-valley. Lakes formed by the subsidence of 

 part of a river valley must digitate into the side valleys. Contrary 

 to this, the side valleys of the great Alpine lakes are not drowned 

 at all, but they are hanging above the lakes, and their floors show 

 no traces of depression. The digitations we find now and then in 

 Alpine lakes have nothing to do with the drowning of true lateral 

 valleys; they do not stretch toward the mountains from which the 

 side valleys come, but extend in the opposite direction. They are 

 related to the frequent valley bifurcations, which will be considered 

 later. 



The basins of the great Alpine lakes occupy only a part of the 

 troughs of the Alpine valleys, and every hypothesis as to their forma- 

 tion must deal with the trough. The trough bears every evidence of 



